skepticism vs doubtfulness

skepticism and doubtfulness both are nouns.

Word	Noun	Adjective	Verb	Adverb
skepticism	Yes	No	No	No
doubtfulness	Yes	No	No	No

As nouns, doubtfulness is a hypernym of skepticism; that is, doubtfulness is a word with a broader meaning than skepticism:

Other hypernyms of skepticism include doubt, dubiety, dubiousness, incertitude, uncertainty.

skepticism (noun)	doubtfulness (noun)
doubt about the truth of something	uncertainty about the truth or factuality or existence of something
the disbelief in any claims of ultimate knowledge	the state of being unsure of something